Numerical investigation in the Brazilian multipurpose reactor pool

The open pool Multipurpose Brazilian Reactor (RMB) project consists of a 30 MW multi application neutron source reactor to attend the Brazilian needs for radioisotopes production and researching. The present concept consists of a 13 m deep cylindrical pool with four main circulation systems: pool, core and heavy water cooling, and hot water layer (HWL). A heavy water reflector vessel is used together with beryllium to enable the extraction of neutron beams. A HWL of 1.5 m that is maintained purified and hotter than the remaining water is used at the top of the pool to reduce the radiation dose inside the reactor building. To analyze the flow behavior in present RMB concept, Computational Fluid Dynamics (CFD) simulations were performed. To simulate the reactor two models were created: core and pool models. The results obtained in the simulation of the core model were exported and inserted as boundary conditions in the pool model. This division was useful in the simulation allowing the use of different time steps, decreasing the total time of simulation. The simulation results show that the mixing in the HWL caused by the pool convection and flow interactions with the chimney were sufficient to reduce the thermal stratification and consequently the radiation shielding in the first moments of operation. Afterwards the HWL begins to reestablish and slowly returns to its initial state. This study shows that the development of a CFD simulation procedure can be very useful, providing relevant data for the development of the R MB project. (author)